age = input('请输入你的年龄：')
if age.isdigit():  # 判断字符串里是否都是数字
    age = int(age)
    if 0 <= age <= 120:  # 等同于age>=0 and age<=120
        print('输入正确！')
    else:
        print('输入有误！')
else:
    print('请输入阿拉伯数字！')